Process for producing pressure-sensitive transfer sheets

ABSTRACT

A PROCESS FOR PRODUCING A PRESSURE-SENSITIVE TRANSFER SHEET HAVING AN ESSENTIALLY COHERENT BUT PARTICULATE TRANSFER COLOR-YIELDING LAYER ADHERENT TO ONE FACE OF A SHEET SUPPORT, COMPRISING THE STEPS OF PROVIDING A FINE COLLODIAL SUSPENSION IN WATER OF PIGMENTS AND FILLERS, OF PROVIDING A COLLODIAL SOLUTION OF WATER OF A FILM-FORMING MACROMOLECULAR SUBSTANCE CAPABLE OF IRREVERSIBLY PRECIPITATING UPON DEHYDRATION OF THE SOLUTION, OF MIXING SAID SUSPENSION AND SOLUTION, OF FORMING A LAYER OF THE RESULTING MIXTURE ON SAID FACE, OF CAUSING PROGRESSIVE ELIMINATION OF THE WATER FROM SAID LAYER TO PROMOTE FORMATION ON SAID FACE OF AN ESSENTIALLY DRY FILM WHEREIN SAID PIGMENTS AND FILLERS ARE EMBEDDED INTO A PRECIPITATED MACROMOLECULAR PELLICULAR STRUCTURE.

p 1972 5. CECCONI 3,692,556

PROCESS FOR PRODUCING PRESSURE-SENSITIVE TRANSFER SHEETS Filed May 24, 1968 I N VE NTOR.

o Ceca 0 United States Patent 01 fice US. Cl. 11736.1 11 Claims ABSTRACT OF THE DISCLOSURE A process for producing a pressure-sensitive transfer sheet having an essentially coherent but particulate transfer color-yielding layer adherent to one face of a sheet support, comprising the steps of providing a fine colloidal suspension in Water of pigments and fillers, of providing a colloidal solution in water of a film-forming macromolecular substance capable of irreversibly precipitating upon dehydration of the solution, of mixing said suspension and solution, of forming a layer of the resulting mixture on said face, of causing progressive elimination of the water from said layer to promote formation on said face of an essentially dry film wherein said pigments and fillers are embedded into a precipitated macromolecular pellicular structure.

BACKGROUND OF THE INVENTION This invention relates to a process for producing pressure sensitive transfer paper sheets provided with a coloryielding layer which can transfer script characters or marks, impressed either manually or typewritten on the front face of the paper itself, on the front surface, provided with suitable receiving layer of which an immediately underlying sheet is provided.

Such transfer papers are well known in the art, and their popularization and utilization is more and more expanding. They are designed to provide a plurality of copies without the use of any intermediate transfer or carbon paper sheets between the superposed sheets, the uppermost one of which is designed to constitute the original one, and the underlying the related copies. The advantages consequent upon the use of such transfer papers known in trade as self-copying papers are many and refiect both economical service aspects and technical aspects as to neatness in the execution of the copies, possibility of obtaining a very high number of copies, elimination of the operations and inconveniences incidental to the use of the intercalated carbon paper sheets, and others. The notoriety of the said self-copying papers and their advantages makes any detailed description thereof superfluous.

For a better understanding of the invention, it is on the other hand advisable to shortly remember that some known production methods of said papers, and particularly of the pigmented transfer layer thereof (constituting the part of prevalent technical interest) are based upon the formation of said layers by coatings of resins including organic and inorganic pigments, which coatings build a particularly rigid continuous film. Such film does not show, generally, sufiicient sensitiveness and selectivity of the transfer, on the receiving layer of the underlying sheet, of the pigmented particles precisely localized in the defined small areas wherein the pressure due to the manual writing or typewriting is applied. In order to avoid such inconveniences, it is well known to promote the formation of discontinuous transcribing layers with the use of polymer solution in organic solvents, and plasticizers adapted to ace as coagulating means for the polymer, so as to minimize the mechanical strength of the film and to lead to the formation of a substantially heterogeneous Patented Sept. 19, 1972 layer. Such plasticizers, consisting generally of oily substances, lead to softening of the layer, which is consequently more subject to soiling during the manipulation of the paper and contamination of the surfaces with which it comes in contact.

Furthermore, such plasticizer, while penetrating the fibers of the paper support, impair the rigidity thereof and makes it undesirably flabby.

The use of organic solvents further results in several inconveniences. For example, they are of difiicult and also dangerous to handle and use on account of their combustibility, of the production of dangerous gaseous products, and others. Furthermore, such solvents, being partly retained in the polymer film even after apparent drying, and evaporating most slowly in subsequent times, lead to sweating and migration phenomena, particularly if assisted by different temperature and ambient relative conditions. Such phenomena lead among other things to the production of trimmings and blurring of the printing inks of typing ribbbons and ball point pens, due to partial solution of relative dyes.

BRIEF SUMMARY OF THE INVENTION With the foregoing in mind, it is the object of this invention to provide an improved process for producing transfer or self-copying papers, as above and more particularly for the formation of transfer layers and/or protecting and masking layers, said process not involving the above-outlined and other inconveniences encountered in prior art, in addition to the advantages inherent in their manufacture according to the aforesaid process, show the most favorable aspects as to conservation and storage, manipulation and service.

The process of this invention advantageously applies to the formation of layers on support means consisting of paper sheet or other sheet material such as plastic sheet. On the other hand, in the present manufacturing fields of said transfer sheets with paper support means, of a predominantly cellulose nature, the process according to this invention advantageously permits to carry out the formation of the layers in the final steps of the manufacture of the papers themselves by particularly adopting adaptations and variations of known technical means, such for example as in the manufacture of the so-called patinated papers."

The technical and industrial advantages consequent upon such a possibility are obvious and apparent to all those skilled in the art.

It is a further object of this invention to produce selfcopying papers which, in addition to the advantages consequent upon their manufacture by the process according to this invention, afford further important advantages, such as a substantial insensitivity of the end product to the action developed by other solvents and by the ambient humidity, by the absence of organic solvents and oily substances, such as the secondary plasticizers, leading to the alteration of the characteristics of the cellulose fibers and however of the paper support means, a great insensitivity and selectivity of the transcribing layer, due to a condition of heterogeneity of microscopic and submicroscopic grains in the pigment conglobating film (that is the film conglobating colored or not colored pigments) and finally the presence of a very dry and particularly smooth transcribing layer, such as not to give rise to soiling and contaminations in the course of the manipulation and the use of self-copying material.

Essentially, according to the present invention, the process is characterized by the formation of the transcribing layer with the use of a colloidal mass in aqueous vehicle, including hydrosoluble pigments and film-forming agents capable of irreversible precipitation in said vehicle during the progressive elimination thereof, so as to obtain an heterogeneous but essentially coherent film in which the pigments are embedded and evenly distributed, and in which the discontinuity is due to the presence of the particles of the precipitate.

Preferably, such colloidal mass also includes wax-like substances in aqueous emulsion, capable of particularly imparting the layer its most desirable surface properties.

Such layer includes, according to prior art, dark pigments, adapted to provide the necessary coloring and contrast in the mark or copy transferred onto the underlying receiving layer, fillers and white pigments or clear pigments. Also according to current principles and knowledge the coating of paper or sheet may include two superposed layers, the outer layer of which not incorporating dark pigments and having the scope of masking and protecting the colored pigmented layer, at least one and preferably both said covering layers being obtained with the use of said process as above defined.

The fact that such process does not include the utilization of organic solvents and plasticizing oily substances leads to some of the aforementioned important advantages and objects of the present invention. For example, the elimination of organic pigments makes the presently necessary utilization of expensive explosion-proof plants superfluous, inasmuch as the solutions, the dispersions and emulsions in water do not obviously lead to dangers of ignitions and/or explosions and however spontaneous and accidental combustions. From such technical conditions principally arises the advantageous possibility of application and formation of the layer in the plants for and during the same paper manufacture by continuous machines, and before such paper reaches its last drying stages. The consequent direct manufacture of self-copying papers in the paper mill enables the elimination of plants and subsequent progressing operations, not excluding obviously and possibly of subsequent formation of said layers on commercially available papers and supports. The elimination of the use of organic solvents, which are not generally recoverable as being dispersed during the drying of the layers, leads, in turn, to not negligible economical advantages with regard to both the cost of said solvents and the cost of plants which should necessarily include suction, picking up and exhausting means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to a preferred embodiment form of the process according to the present invention, said colloidal mass in vehicle of aqueous nature is obtained by the association and intimate mixing in a suitable mixer of different previously and separately arranged components, i.e.:

(a) A fine colloidal suspension, in water, of pigments and of fillers, particular mineral substances the particles of which, even if very little, retain in the suspension their original structure. The stability of the suspension may be assured by emulsifying means and dispersing agents (peptizing agents). Such suspension is prepared by active subdivision carried out mechanically of the pigments through grinding and by the use of turbo-dispersing agitators.

In respect to the pigment choice, it is advantageous to take into account the Wettability and dispersibility of the same in aqueous vehicle, which characteristics are imparted by the fineness (on the order of 1-10 microns) and by the diameter of the aggregates identifiable in the dispersion. Particularly, among titanium oxides there are preferred the post-treated types based on SiO and A1 for increasing their stability to the light, as well as improving their wettability and promoting the formation of finer and more uniform dispersions with the least mechanical work.

As filler one may advantageously use talc, magnesium silicate, barium sulphate, zinc sulphate, mica, kaolin, bentonite, clays, precipitated alumina, and silica, besides titanium oxide, such fillers or at least a part thereof having obviously the function of acting as masking or covering clear pigment. The most part of these compounds has a bidimensional structure, and as such they foliate, forming lamellar particles. The bidimensional planes are sealed by water molecules and OH ions, and hence their surface has a strong atfinity with these both components. In such case, there is a more or less acid reaction as a consequence of the increase in the concentration of H+ ions within the solution, because of the absorption of OH- ions on the particle surface.

That leads to the formation of a double layer formed by absorbed OH- ions and cations of the salts which are always present in the solution. The water molecules, having considerable dipole moment, set themselves in the double layer area so as to orient the H+ ions toward the pigment surface and the O- oxygen-ions toward the outside. Such phenomenon is exploited for the purposes of the process according to this invention, inasmuch as it leads to an actual alteration of the aqueous phase of the suspension, in a substantially orderly structure form, with substantial stiffening of the molecules, which lose a great part of the mobility possessed in liquid phase. The forma tion of sedimentations and agglomerations, as would be otherwise hardly avoidable in the aqueous suspensions, is thus avoided.

The dark pigments, designed to ensure the visibility and the contrast effect in the copies, are preferably constituted of carbon blacks, that is of well known amorphous absorbing compounds formed of mixtures consisting of carbon and hydrocarbons of different nature, adapted to give the suspension and hence the transcribing layer produced with the same in the most suitable concentration the required dark tonality.

Such carbon blacks are preferably selected from those obtained according to the Channel method due to both reduced particle dimensions (9-29 microns) and their low pH, which makes them more easily emulsifiable in water. Such dark pigments are commercially available under different trade names, such as Carbolac, Monarch and Mogul (Cabot Corporation), Regent and Printex (Degussa) and Spectra (Columbian Carbon Company).

The dispersion and the stability of the colloidal suspension is preferably ensured by suitable emulsifying and tension active agents, such as polyoxyethylene ether of nonyl phenol, polyoxyethylene sorbitan monoleate and monolaurate, sorbitan monoleate and polymethylene lauryl alcohol. Such compounds are commercially available under different trade names, such as Giten, Renex, Brig and Tween.

(b) A macromolecular colloidal solution, designed for the formation of the film and binding vehicle. Such colloidal solution, prepared in a suitable known equipment, comprising preferably heating and slow agitating means, is constituted of a aqueous solution of colloids which should have the following characteristics:

('1) Complete solubility in H O, with consequent exclusion of the resins formed by groups of prevalently homopolar characters (CH CH C H which are generally soluble in organic solvents. Consequently colloids are being used, containing many hydrophilious groups (NI-I COOH, CO, OH), which are generally hydrolyzable, and therefore products showing the characteristic of being insoluble in organic solvents, but soluble in water, giving hydrosols.

Generally, such ion generating groups are attached to any fundamental molecule, forming macroanions (polyanions and polycations) which determine the presence of surface charges, thus giving way to a double electric layer.

(11) Accentuated hydrophilis character, that is having the property of causing the molecules of the dispersing means to adhere to its own surface and then to solvate, so as to build around the macromolecular particles a more or less thick mentle of H 0 which impedes the mutual contact and union.

(III) Isodimensional structure, that is with macromol ecules extended in the three dimensions or linear structure with short molecules and low viscosity. Such colloids occur at their solid state as pulverulent masses of amorphous aspect and with equal properties in the three dimensions. To the contrary of the fibrous resins with most elongated molecule, they are unable to build films of strong mechanical strength, not advantageous for the purposes of the present invention, because such films would show an excessive strength to their selective fragmentation, necessary for localized selective transfer to the underlying receiving layer in the course of the copy execution. Such limited mechanical resistance of the films ensures consequently to eliminate (according to an important object of this invention) the use of both primary and secondary plasticizers, which are presently considered necessary for the formation of operable transfer layers of the selfcopying papers considered.

The colloidal substances utilizable may be selected from the natural products (animal proteins, bone glue, fish glue, lactic casein, ovalbumin or others), from the algae extracts (sodium and potassium alginates) and rice starches, wheats, potato feculae and maize.

Such products should be degraded, namely reduced to a short molecular chain, and treated so as to increase their solubility e.g. chlorodized, hydrolyzed, oxidized, esterified or sulphurized. Products of this kind are commercially available, for example under the trade names Farinex, Calfarex and Milgum. The white or yellow dextrine and the arabic gum may be used.

Synthetic products may also be made use of such as formaldehyde urea and formaldehyde phenol, which products have a particular aflinity with hydroxyls of the cellulose of the paper support, and which by binding therewith increase the resistance to humidity. One may finally utilize some cellulose derivatives, such as methylcellulose, carboxy-methyl-cellulose, monoacetyl-cellulose and xanthogenate of cellulose.

For the purposes of attaining the objects of this invention, of particular interest is the initial stability of the macromolecular colloidal solution, as well as the formation of the same and in the layer being dried, of precipitates adapted to impart to the binding vehicle of the layer or coating the desired microscopic homogeneity, which is advantageous to ensure the maximum sensitivity and selectivity in the transfer and formation of the copies. A few considerations are therefore added to better illustrate the conditions under which the desired phenomena are taking place and to comment on the means cooperating to the development thereof.

The stability of the colloidal solution is influenced by different factors: primarily by the probability of the shocks between the molecules, due to the Brownian motion and therefore by the temperature and the viscosity of the medium. Consequently, by suitable heating, it is possible to promote and/or contribute to the precipitation of the colloid into very fine grains and separation of the solid phases, with the increase of the kinetic energy of the molecules, because the increase of the molecular motion, particularly combined with the increase of the colloid concentration and/or dehydrating agents, leads to an increase in the number of shocks between the particles and the weakening of the aqueous mantle due to the hydrophilic nature of the macromolecules.

Such stability is further influenced by electrolytes capable of developing a fiocculating action, inasmuch as they lower the electrokinetic potential of the double charge layer.

When such potential reaches a minimum value (critical potential), there occurs precipitation of the colloid (isoelectric point).

Such fact is to ascribed to the hydration proper of the salt ions, that is to say, to the property which such ions possess to orient about them the dipoles of H 0, forming therewith more or less labile aggregates. In the particular case of this invention, including the use of hydrophilic colloids, their stability is controllably reduced by acting on their solvation by demolition with dehydrating means of the solvated mantle, so as to obtain a partial flocculation which under ordinary ambient conditions turns out irreversible. Obviously, this phenomenon is accentuated in the smearing and drying phase of the colloidal mass.

Consequently, according to a significant feature of this invention, to said colloidal mass there are associated dehydrating means and electrolytes, particularly the latter in the necessary measure to reach a value near the critical potential, but without exceeding at least in sensible measure the isoelectric point, so as to lead the colloids to the minimum solubility condition and maximum sensitivity to the precipitating agents, occurring upon the production of fine precipitation phenomena, without however undesirable coagulation or amassment phenomena of the particles, and therefore to obtain the formation of the desired discontinuous layer of very thin grain.

Consequently, in order to promote the development of the desired phenomena of precipitation, according to this invention, suitable combinations and associations of the following factors are being exploited:

Use of electrolytes, adapted to reduce the surface charge of the macromolecules in solution;

Use of dehydrating means adapted for the demolition of the solvated mantle;

Use of acids and bases to reach the desired pH in the solution and the paper, in which the instability and hence precipitation conditions occur;

Heating action in drying phase, so as to increase the kinetic energy of the molecule and therefore the number and the intensity of the molecular shocks;

Exploitation of the progressive concentration of the solution, in drying phase, also to statistically increase the probability of the molecule shocks.

As dehydrating means, one may use ethyl alcohol, ace tone, glacial acetic acid, trichloroacetic acid, sulphosalicylic acid, and others.

As electrolytes one may use the ammonium sulphate, sodium sulphate, magnesium sulphate, as well as the chlorides of the same metals, and the ferric compounds, the electrolytes having to be selected on the basis of their ac tivity, and by taking into account of the pH corresponding to the isoelectric point of the utilized soluble colloids.

(c) A wax-based aqueous emulsion. Such emulsion has the purpose of improving the chemical-physical character istics of the layer, particularly imparting the following properties to the transcribing layer:

Resistance to humidity, both in the layer and the paper support, due to the typical hydrorepellency of the waxes;

Brightness and brilliancy of the surface;

Improvement in the chemical-physical alfinity with the receiving layer on which and in which is effected the transfer of the pigmented particles, during the execution of the copies;

Exercising of a complementary action as binder and also plasticizer.

According to the essential feature of the process of this invention, excluding the use of organic solvents, and practically providing that the substance designed for the formation of the liquid phase of each component is exclusively water, there are therefore excluded wax solutions, and the consequent problems are resolved by using wax emulsions in water. Such emulsions consist of aqueous dispersions of microscopic wax particles, maintained in suspension by emulsifying agents.

Such emulsions, for the practical purposes of the accomplishment of the process, behave like solutions. As a matter of fact, they may be diluted with H O, applied on dry or wet material, and particularly incorporated in the wet process manufacture. The water, being subsequently eliminated from the treated material, leaves a very thin Wax layer, possessing also desired properties.

The emulsions may be obtained by suitable emulsifying equipment, including heating and quick agitating means, with paraflin, petroleum and micro-crystalline waxes and however preferably with non-ionic matters for obtaining a better stability to the different acidity and alkalinity conditions. Several suitable waxes are commercially available, such as Mobilcer of the types A, P and Q (Mobilco) Alvax (Du Pont) and the Hoechst Waxes of the types E, S, L, LP and KPS. As wax material, polyethylene suspended in soaps may be used, such as the oleic acid, palmitic acid and stearic acid, in combination with amines.

The colloidal mass may further comprise secondary fiixing and/ or cooperating agents for the purposes of the resistance to water, such as the formaldehyde, the boric acid and others; also softem'ng agents may be added, such as the glycerine and the solid polyglycols with high molecular weight.

As Well known, the properly pigmented black layer, designed to provide visible and contrasting copies, may be protected and masked by a white or clear covering layer, showing similar characteristics to those of the dark layer in order to assure compatibility for the purpose of the selective particle transfer. Such covering layer should be distinct from the underlying black layer, while still having the capacity of fixing thereto, and it is necessary for it not to appreciably alter the intensity of the reproduction and the tonality of the copy writing.

In practice, there exists no distinction of the preparation and application techniques between the inked black layers and the clear covering layers. Practically, the latter are prepared as indicated above, obviously with exclusion of the carbon black and however of the black pigments, clear pigments possessing in a larger measure covering properties, such as the titanium oxides, being preferred.

On the accompanying drawing are schematically reproduced the main combinations and sequences of the essential phases of the process according to this process, particularly:

FIG. 1 represents schematically and in part in flow sheet form the complete execution of the process, and

FIGS. 2 anud 3 show, still schematically, two embodiments of the means for and the step of application and formation of the layers.

As shown in FIG. 1, A, B and C designate schematically the means for the preventive independent preparation of the components referred to above, namely of the fine colloidal suspension of the pigments and charge matters in Water, and respectively of the macromolecular colloidal solution, in water, and of the emulsion still in water of the cerous substances.

Such essential components are caused to flow into a mixing environment M, in which are, in turn, added the dehydrating agents D and the electrolytes E, in addition to the eventual cooperating, fixing and/or softening means.

The colloidal mass provided in a mixing environment M is applied in thin layer or film form to the laminar sup port L for example by means of a smearing roller S, provided with dosing blade, and the applied layer, adjusted as to quantity and thickness for example by a scraper Ra, is then dried for example through passage of the laminar support around heated cylinders or rollers R.

The dosed application of the colloidal material Mc, may be carried out by other systems, for example by sprayers Sp, and the layer may be adjusted and uniformized between calendering cylinders R and R", which may also act as heaters, all as exemplified in FIG. 2.

In the modified embodiment in FIG. 3, the laminar material L of support receives the application, by means of an inking roller Ri supplied by an inking system I consisting of cylinders, the layer being dried through the passage around a heated roller R and/or in presence of a radiator Rt provided for example with electrical resistors. In the same FIG. 3 is also exemplified the use of an opposed inking roller Ri', supplied by a proper inking system I for the application of a material M designed for the formation of the opposed receiving layer.

The details of mixing, dissolving and emulsifying means are not described herein, as they are well known in the art.

Also the technical means for the dosed application and drying of the layer or layers are not described because corresponding to those used in the art with the obvious simplification due to the superfiuousness of explosionproof plants and facilities, for the evacuation of the sol vent vapors, of others. In practice, one may utilize the means and plants as currently used for the application and treatment of the surface layers of the patinated papers.

For such reasons, the formerly outlined manufacture of self-copying papers according to this invention, directly in the paper mill, is possible and advantageous, and by using well known plants for continuous production of patinatedtype papers, and the final patinating fraction of said plants for the application of the characteristic layers of the selfcopying papers.

A few examples follow as indication of the practical accomplishment of the invention.

Such example are subdivided into groups regarding the composition of the above-discussed three essential components in aqueous vehicle, and then examples of final compositions are given by dilferent combinations and associations of said components, together with eventual cooperating substances.

Such examples are grouped in form of tables in order to ease a comparative examination.

All examples given in the following pages relate to components, obviously with exclusion of water, and are indicated in parts by weight, expressed in terms or percentages at solid state.

TABLE I [Examples Ai-Ag (colloidal suspensions a)] Examples for the formation ot' Dark layers A2 A3 A4 Clear layers Components Carbon blacks:

Monarch 71" Mogul A Regent". Printer-r "Neo Spectra Dispersants:

Polyoxyethylene sorbttan monoleate Polyoxyethylene sorbitan Bentonite. Diatornite Magnesium silicate 30. 0 Zinc sulphidebarlum sulphate 10.0 r 20.0 20.0 Zinc oxide 20.0 20.0 Precipitated calcium carbonate 15.0 Titanium oxide,

post-treated 20.0 Water up to 58. 5

All dark pigments, above indicated by their trade names, can consist of low pH carbon blacks produced by Channel process and of dimensions comprised between 9 and 29 microns.

Ovalbunn'n I Yellow dixtrine Sodium alginate. Chlorodized rice starch Oxidized potato fecula Formaldehyde urea Solution cooperating means:

Ammonium hydrate 1 Sodium hydrate 0. 1 Water at 100% 84 92 80 90 84 87. 9 85 95 TABLE III [Examples C -C (Wax emulsions c)] Solid con- Melttents ing (perpoint, Example Wax type cent) 0. Commercial wax C1 Paraffin and 48-53 60 Mobilcer A.

petrolate. C2 Petrolate 39-44 72 Mobilcer p. Cs Mlcrocrystall 49-53 70 Mobilcer Q. C4 Parafiin-vinyl 50 70-75 Alvax 253-6 resin. C do 45-50 75 Elvax PB3- 1201. C Basic Montan 20 80-83 Hoechst S.

wax. C7 .do 10-20 78-82 Hoechst E. C; do 10-20 78-81 Hoechst PE.

The waxes referring to Examples C -C are available on trade as emulsions with the above mentioned solid contents. By using Montana waxes it is instead necessary, generally, to provide for the preparation of the relative emulsion.

A number of examples are provided in the following pages of colloidal masses obtainable by different combinations of colloidal suspensions and wax emulsions, all in aqueous vehicle, according to the preceding examples. Consequently, in the following examples the compositions of the colloidal mass will be indicated in parts in weight by making simple reference to the examples given in the preceding Tables I, II and III and with the addition of dehydrating means (indicated with D), of the electrolytes (indicated with E) and various cooperating means (indicated with C) having an emollient, hardener, fixer and others function.

Consequently, the following examples represent the contents of the mixing environment M, schematically outlined in FIG. 1, and from which the layer formation composition is issued.

In the following examples, Examples I-V represent colloidal masses and mixtures adapted for the formation of a dark transfer layer, designed for transfer with formation of neat and sharp copies, whilst the Examples VI-VIII give compositions adapted for the formation of white or clear coating, protecting and surface completing overlayers for the transfer dark layer.

Example I Parts by wt. Colloidal suspension of Example A 70 Colloidal suspension of Example B 12 Wax emulsion of Example C 13 D: sulphosalicylic acid 4 E: sodium sulphate 1 Total 100 Example II Parts by wt. Colloidal uspension of Example A 62 Colloidal solution of Example B l0 Wax emulsion of Example C 15 D: ethyl alcohol 9 E: ammonium sulphate 2 C: glycerine 2 Total F70 Example III Parts by wt. Colloidal suspension of Example A 65 Colloidal solution of Example B 16 Wax emulsion of Example C 13 D: glacial acetic acid 5.5 E: barium chloride 0.5

Total To Example IV Parts by wt. Colloidal suspension of Example A; 5 8 Colloidal solution of Example B 20 D acetone 10 E potasium nitrate 2 C polyglycol, M.W. 4000 10 Total TOT) It may be observed that in the above Example IV the wax emulsion, is not included in that the composition character does not necessarily require the use.

Example V Parts by wt. Colloidal suspension of Example A 69 Colloidal solution of Example B 10 Wax emulsion of Example C 11 D: trichloroacetic acid 8 E: amomnium sulphate 2 Total 3% Example VI Parts by wt. Colloidal suspension of Example A 41 Colloidal solution of Example B 15 Wax emulsion of Example C 30 D: ethyl alcohol -n 12. D: pentadigalloil-glucose 1 C: polyglycol, M.W. 4000 1 Total F10 Example VII Parts by wt. Colloidal suspension of Example A, 43 Colloidal solution of Example B 15 Wax emulsion of Example 0; 30 D: acetone 10 E: potassium nitrate 2 Total W) Example VIII Parts by wt. Colloidal suspension of Example A 45 Colloidal solution of Example B 8 Wax emulsion of Example C 30 D: ethyl alcohol 15 C: formaldehyde 2 Total at As it may be observed in this Example VIII, no electrolytes are being used for contributing to the formation of the precipitate of the colloidal solution, since, in view of the composition adopted, the dehydrating will act as an agent for the demolition of the solvated mantle of the macromolecules in solution.

Obviously, the above shown examples represent only some of the possible embodiments of the invention, and it should be understood that any other embodiment of the process according to this invention, both as to the different association and combination of the essential components and the different formation of said components, with the characteristic of the absence of organic solvents, the preparation of the colloidal mass in exclusively aqueous vehicle (obviously except the addition of dehydrating agents and/ or electrolytes) and the application of the equally characteristics concepts of formation of a 'very fine precipitate of the organic solutes, particularly proteinic, for obtaining a coherent but discontinuous layer still remaining firm and unchanged, be comprised within the scope of the present invention.

1 claim:

1. A process for preparing the transfer layer of selfcopyin-g paper which comprises the steps of (l) applying to a support a colloidal material in an aqueous vehicle, said colloidal material consisting of a mixture of (a) a colloidal aqueous suspension of pigments and filler materials, (b) a colloidal aqueous solution of water-soluble film-forming macromolecular compounds capable of irreversible precipitation in said vehicle, (c) an aqueous waxy emulsion, (d) a dehydrating agent and (e) an electrolyte, (2) adjusting the pH to the range at which said irreversible precipitation occurs and (3) progressively eliminating said vehicle by heat so as to obtain a heterogeneous but coherent film in which the pigments are distributed.

2. A process, according to claim 1, wherein said colloidal aqueous suspension includes compounds having an acid reaction.

'3. A process, according to claim 1, wherein said colloidal aqueous suspension is stabilized by emulsifying and surface-active agents.

4. A process, according to claim 1, wherein the colloidal aqueous solution is formed of colloids containing hydrophilic groups N11 COOH, CO or OH, which colloids are substantially insoluble in organic solvents.

5. A process, according to claim 4, wherein the colloidal aqueous solution is formed with colloids having a structure which is substantially isodimensional.

6. A process, according to claim 5, wherein animal proteins are used as said colloids for forming said colloid-a1 aqueous solution.

7. A process, according to claim 4, wherein there is added to said colloidal aqueous solution dehydrating means for the destruction of the solution of the hydrophilic colloidal substances in the colloidal solution.

8. A process, according to claim 3, wherein there are added, to the colloidal material, electrolytes for lowering the electrokinetic potential of the colloidal solution to a value near the isoelectric point thereof.

9. A process, according to claim 3, wherein heat is applied for facilitating the elimination of the aqueous vehicle.

10. A process, according to claim 1, wherein the transfer layer is formed in the final stage in a process for the continuous manufacture of the paper support.

11. A selfcopying paper having a transfer layer produced by the process of claim 1.

References Cited UNITED STATES PATENTS 3,03 6,924 5/ 1962 Newman 11736.1 3,382,088 5/1968 Noda 117-361 3,380,882 4/1968 Boyer et a1 161-242 1,965,257 7/1934 Poschel 1l7-36.1 X 2,772,175 11/1956 Beatty 106-24 X 2,868,741 1/ 1959 Chambers 106-24 X 3,065,099 11/1962 Newman ll7-36.l 3,337,361 8/1967 La Count l1736.1 3,446,647 5/ 1969 Rizner ll73'6.l 3,472,674 10/ 1969 Kite 1l736.1

WILLIAM D. MARTIN, Primary Examiner W. R. TRENOR, Assistant Examiner US. Cl. X.R.

ll736.2; l0624, 31 

